1. Field of the Invention
The present invention relates generally to switch mechanisms and, more particularly, to switch mechanisms which incorporate a cam surface shaped to provide a damper so that overtravel of a switch plunger can be prevented when the plunger is suddenly released from a depressed position.
2. Description of the Prior Art
Many types of switch mechanisms are well known to those skilled in the art. A particular application of switch mechanisms of this type relate to pushbutton switches that comprise a plunger that is moveable relative to a base along an axis and which causes actuation of switching components when the plunger is depressed. Typically, the plunger is connected to a button that is depressible by a human finger. Some switch mechanisms cause actuation of a switch upon each depression of the button and plunger while other switch applications, referred to as alternate action devices, actuate on one push and release of the button and undo the actuation on a subsequent push and release of the button.
Regardless of the specific application of the switch mechanism, most known mechanisms utilize cams and cam followers to control the sequence of operations resulting from depression of the button and plunger. U.S. Pat. No. 4,254,315, which issued to Stevens on Mar. 3, 1981, discloses a pushbutton switch with a safety stop. The switch utilizes a locking mechanism that includes a cam member with a groove of the cam member being engaged by a cam follower. The groove is in the form of a closed loop path and the pushbutton is linked to the locking mechanism so that movement of the pushbutton moves the cam follower relative to the cam member along the groove. The cam follower moves only in an up and down direction in line with the axis of movement of the button and the cam moves in a direction perpendicular to that axis.
U.S. Pat. No. 3,523,168, which issued to Holmes on Aug. 4, 1970, describes a pushbutton switch which has a positive plunger safety stop carried in its casing. The switch has a tubular casing that receives a pushbutton at the upper casing end and has a lower switch at the lower casing end. The pushbutton is moveable inward into the upper casing end by an initial pushing inward followed by moving upwardly by a release counterspring action. The switch comprises a plunger guide that can have a plurality of grooves in which teeth of a plunger disc reciprocate vertically so that the plunger can not substantially rotate relative to the plunger guide. The guide has an upper circular edge above the grooves and the guide is enlarged radially outwardly to provide shoulders to hold the upper end and the lower bottom of the plunger guide between a lamp contact block and the bottom of a casing structure.
One serious problem that can occur during the operation of a pushbutton switch is the sudden release of the button while it is fully depressed relative to its housing. Since most pushbutton switches utilize one or more compression springs to urge the button and plunger outward relative to the case or housing, a sudden snap-release of the button can result in the rapid movement of the plunger and button away from the base of the switch to result in the button exceeding its normal unactuated position. In some extreme cases, the pushbutton and plunger can actually disconnect from the housing and be projected out of the pushbutton housing. In less extreme, but equally deleterious circumstances, the pushbutton can become separated from the plunger while remaining within the housing. The subsequent actuation of the device will require an initial force to reconnect the pushbutton and plunger followed by another force to actually actuate the device. Another possible result from a sudden snap-release is the movement of the plunger to a position normally assumed only during a relamping procedure as provided for in U.S. Pat. No. 4,254,315 described above and in U.S. patent application Ser. No. 973,132 which was filed by Cummins and Shaw on Nov. 6, 1993 and assigned to the assignee of the present application. The plunger could react to a snap-release by moving to the relamping position and require two sequential forces, separated by a release, to actuate the device. All of these possible results are seriously disadvantageous.
In view of the above problem, it would be significantly beneficial if a means were provided to prevent this type of overtravel in response to a snap-release of a button and plunger of a pushbutton switch.